1. Field of the Invention
The present invention relates to a driving force transmission mechanism for transmitting a rotation driving force to a rotation member, and relates to an image forming apparatus using the driving force transmission mechanism.
2. Description of Related Art
Conventionally, in an image forming apparatus such as a copier, a printer, and a facsimile machine, various rotation members are used. In order to rotate such rotation members, it is necessary to transmit a rotation driving force to each rotation member from a drive source such as a driving motor (not shown). Accordingly, in a driving force transmission mechanism for transmitting the rotation driving force, a multi-step gear having a large speed reduction ratio is disposed between a gear coupled to the driving motor rotating at high speed and a gear provided onto each rotation member, and reduces rotational speed of the each rotation member.
Conventionally, in the driving force transmission mechanism described above, the multi-step gear is supported by a cantilever shaft, and a distance between a center of the multi-step gear and a center of the gear provided onto the rotation member is kept constant. However, in a case of using the cantilever shaft described above, when large load is applied to the multi-step gear, the shaft is bent so that the distance between the centers cannot be sometimes kept constant. As a result, irregular rotation of the rotation member occurs, and there is a fear that image defects caused by the irregular rotation are generated.
In this context, in a drive train to which large load is applied, and in a drive train for which highly accurate rotation is demanded, there is used a driving force transmission mechanism in which both ends of a shaft for holding the multi-step gear are supported. That is, a free end of the cantilever shaft, which is provided so as to protrude from a support portion, is held by a frame or a holder so that both the ends of the shaft are supported. Thus, even in the drive train to which large load is applied and the drive train for which highly accurate rotation is demanded, it is possible to keep constant with high accuracy the distance between the centers of the gears.
As such structure in which the distance between the centers of the gears is kept constant, for example, the following cantilever shaft holding device is given. In the cantilever shaft holding device, a plurality of penetration holes are provided around a holding hole of a shaft support member, and the cantilever shaft is caulked after caused to pass through the holding hole, to thereby be fixed to the shaft support member. Then, after both the ends of the cantilever shaft are positioned, the shaft support member is fixed to another member. With this configuration, the cantilever shaft holding device can increase caulking strength of the cantilever shaft with respect to the shaft support member, and absorb positional displacement of the cantilever shaft by allowing the cantilever shaft to easily bend.
However, the multi-step gear to which large load is applied and the multi-step gear for which highly accurate rotation is demanded are often meshed with a gear provided onto the rotation member that generally serves as a last output portion. Accordingly, in a case of using the attachable/detachable rotation member, it is necessary to provide an attachment/detachment space for the rotation member, and hence it is difficult to provide a space for holding both the end portions of the shaft in the apparatus main body.